1. Field of the Invention
This invention relates to a method and a device for separating nondesired objects from a product flow. In this method an emitted broadbanded light is absorbed differently in the surface of the objects. The difference in absorption decides which type of objects is detected.
2. Background Art
In for example agriculture and horticulture there is a great need of separating contaminations such as stone and clods e.g. in potatoes and onions. Today there are manual assortment and mechanical systems with spike mats and brushes. Stones in potatoes and onions have always been a great problem. In the last two decades various mechanical stone separating devices have been developed. The two main problems of these are that mechanical separation, e.g. by means of brushes, will cause a great damage to the potatoes and it is difficult to get a mechanical system functioning satisfactorily under varying soil conditions. In electronic stone and soil separation the contaminations are removed when falling freely which eliminates the damage to the potatoes completely. Manual assortment is expensive and not quite satisfactory in view of working environment. In another method used today all stones are screened off and put between the rows of potatoes. The disadvantage of this is that the stone retains the soil moisture and the heat in the soil. In wet weather the soil will dry more slowly without stone content which delays the harvest.
In indoor assortment of potatoes there is also a need of an efficient assortment. Potatoes having green stains are today assorted quite manually at roller tables, a method that does not give a perfectly satisfactory result. A better result can be obtained by the method and device described above with a field of vision from two directions. Internationally there are many agrigultural products that can be assorted according to color. Our method and device provided with suitable filters and detectors can be seen to be of great use there.
When lifting potatoes three to four persons must supplement the mechanical assortment. By this device the capacity of the machine can be increased and the staff of workmen be reduced to one person.